Storage and retrieval machines are commonly used in material and inventory storage facilities for storing items in and retrieving the items from the facilities. Typical of such facilities are warehouses having storage racks of substantial height arranged along aisles in which the storage and retrieval machines travel to various designated aisle locations. The machines are self-propelled by electric drive motors and provided with signals from a remote source to direct them to each aisle location.
At each designated aisle location, there are a number of storage racks arranged in a vertically stacked manner. Each storage rack is typically suitable for holding a single box, pallet, or other items. The storage and retrieval machine inserts items into or retrieves items from each rack by moving a carriage along a vertical mast opposite the vertically stacked racks to a position opposite a designated rack and, by means of a shuttle, moving an object to be stored into the rack or retrieving an object to be moved elsewhere from the rack. A shuttle typically comprises several plates, a base or first one of which is affixed to the carriage. The balance of the plates are extendable from the carriage in a telescoping fashion into a bottom area of the rack space to transfer the box or pallet from the carriage to the rack or remove the box or pallet from the rack and on to the carriage.
The telescopically extendible plates are supported by multiple roller sections moveable in guide ways with either the roller sections or the guide ways for each plate being mounted on an immediately adjacent underlying plate. In extending from the carriage into the bottom area of the rack space or retracting from the rack space to the carriage, the clearance between the guide rollers and the guide ways, along with deflection caused by the weight of the shuttle, causes the shuttle to deflect below the theoretical straight line extension. The amount of deflection increases when a load object is on the shuttle. The historical method to compensate for the difference in deflection, loaded versus unloaded, has been to increase the distance the shuttle is lifted above the rack elevation at which the load is placed. Increasing the distance the shuttle is lifted requires increasing the rack clearance above the load object, thus increasing the space required to store the object. This additional vertical space is required for each vertically stacked rack space to thereby substantially increase the height of the entire rack or result in less rack spaces. To eliminate this wasted space problem, shuttle guide mechanisms have been developed which move the extended plates upward at an angle to deposit or pick up a load object and correspondingly move the extended plates downward to retract a load object from a rack. The present invention is an improvement in this type of shuttle guide for storage and retrieval machines.